(483a) Polymer adsorption in nanopores and nanoporous substrates

Polymer adsorption is a ubiquitous phenomenon occurring in a wide range of disciplines and finding numerous technological and healthcare applications. The mechanisms of polymer adsorption on surfaces and in pores are complex due to a competition of various entropic and enthalpic factors.  Due to adsorption of monomers to the surface, the chains gain in enthalpy yet loose entropy due to confining effects. This competition leads to the existence of critical condition of adsorption when the enthalpy gain and entropy loss are in balance. The critical conditions are controlled by the confining geometry and effective adsorption energy, which depends on the solvent composition and temperature. We present a Monte Carlo simulation study of polymer adsorption in nanopores focusing on the explanation and quantification of the critical conditions. We show that the main contribution comes from the chains located at the external surface of porous substrates. These chains are adsorbed in pores only partially and attain so called “flower” conformations. The incremental gauge cell MC method allowed us to determine the free energies of adsorbed chains and to calculate the partition coefficient as a function of adsorption potential, pore size, and chain length. We found and justified the critical conditions for chain length independent separation in polymer chromatography. Drawing on a case study example of separation of a series of linear polystyrenes, we found quantitative agreement with the experiments.